Traditionally, in a vehicle the loads have to be maneuvered towards the rear opening, the vehicle having been backed towards the loading bay, and the loads removed by fork-lift trucks, and vice versa in the case of loading the vehicle. The area between the rear of the vehicle and the warehouse bay and the transfer between them has not been fully addressed as a problem. Transfer apparatus to replace fork-lift trucks assume greater importance with "just in time" deliveries.
More recently, flexible elements, for example, cable systems, as well as moving belts, chain conveyors, and pushing and pulling devices, have been developed for moving loads inside vehicles for unloading on to roller platforms for transferring to or from the loading warehouse bay.
These known arrangements have a number of disadvantages. In Publication No. WO 87/01996 published under the Patent Co-operation Treaty, a flexible element is attached at one end to one side of a bulkhead and at its other end to the other side of the bulkhead. The bulkhead is driven up or down the interior of a vehicle compartment by sprockets engaging in a chain track which extends down both sides of the container. The driven bulkhead moving along the track thus pulls the flexible elements around non-driven pulleys at the front and back end of the container to convey loads towards the back end of the container or front end.
Although the flexible cables are described as endless in this specification, it is clear that they are not since the ends of the cables are joined to the bulkhead and it is the bulkhead that pulls or pushes the cables.
Similarly, in U.S. Pat. No. 4,111,318, a bulkhead is driven along the floor of the container in one direction by a flexible element, in this case a cable being wound round a drum. The bulkhead is returned to the front end of the container by separate return cables being wound up round further drums. No chain drive system is disclosed in this patent specification.
The present invention aims to overcome the disadvantages of having any form of moving bulkhead and overcomes the need for moving the bulkhead by any form of chain drive or the requirement of a bulkhead track. The disadvantage of a chain drive and a track for the bulkhead is very clear in that these tracks or chains may become embedded with dirt and debris, requiring maintenance and lubrication, and may damage or spoil the cargo which would be unacceptable for food containers.
The moving bulkhead which, in fact, provides some of the thrust to move the load and cable together firstly occupies a not inconsiderable space and reduces the volume of the container. The cross-sectional area of the bulkhead may be a large proportion of the cross-section of the container.
When the bulkhead has been driven to the rear, most of the load will have been conveyed to the docking platform, but the last item cannot be pushed on to the platform because of the presence of the bulkhead. It is quite clear that the bulkhead must be stopped before the opening short of any obstruction such as door closing furniture and cannot pass around and underneath the container. This causes a type of problem described in U.S. Pat. No. 4,111,318 where the pusher bar is required to push the last item so that it is completely on the transfer system on the loading dock.
After unloading, the bulkhead has to be pulled or driven back to the front of the container. In U.S. Pat. No. 4,111,318, this is achieved by separate pull-back cables being wound up on drums. The pull-back cables do not carry the load. Separate motors are required for the cables and difficulties in synchronizing their speed of rotation and hence tension of the ropes needs to be dealt with. In the loading mode, therefore, it is necessary to connect the bulkhead to the load so that the moving bulkhead tows loads into the vehicle. In the unloading mode, the movable bulkhead in the most rearward position needs extra pusher mechanisms to push the load towards the rear end of the container and completely on to the transfer system. Cable drive conveyor systems using moving bulkheads are unsuitable for most transfer systems to be placed between the vehicle and the unloading dock.
U.S. Pat. No. 3,272,358 discloses yet another form of cable arrangement for a vehicle floor for discharging particular bulk loads such as asphalt or grain. The material is drawn out of the vehicle by attachment to cables which operate in the floor of the vehicle. U.S. Pat. No. 3,272,358 does not have a moving bulkhead as disclosed in the other two prior art specifications and overcomes problems associated with moving bulkhead systems but introduce further problems. The floor of the vehicle is provided with a number of separate closed loop cables driven directly by a drum and the cables pass along channels in the floor and under the floor on their return path.
While the cables or flexible elements are of the true closed loop type, that is, the ends of each cable are joined together to form a closed loop, this type of system has other disadvantages. In FIGS. 6, 7 and 9 of U.S. Pat. No. 3,272,358, there is disclosed a modification to enable this system to be used for packages or packaged material in contrast to bulk granular materials. One type of closed loop cable is shown in FIG. 9 in which the cable is a single long loop passing round rollers at each end of the vehicle floor, and then on to the next roller, and so on, and eventually this end of this single cable is taken round pulleys and joined in some way to the other end of the cable. This involves very complicated reeving of cables around the pulleys and includes a section where the cable is moving transversely to the other parts of the cable. The cables run under the floor of the vehicle.
As an alternative, U.S. Pat. No. 3,272,358 discloses a number of separate closed loop cables, again passing under the floor of the vehicle. The use of closed loops requires great care in joining the cables or rope or chains if they are not to break in service with heavy palletised loads for which the present invention is intended. It is believed that maintenance of the cables in this type of system as disclosed in U.S. Pat. No. 3,272,358 would be difficult as regards reeving replacement cables around the pulleys when cable breakage occurs. Furthermore, there are considerable assembly problems in reeving the ropes around pulleys and under the vehicle and splicing their ends together on the vehicle, and extreme difficulties with maintenance when the ropes break requiring access to the underneath of the floor of the vehicle.
Closed loop cable breakage has been found to be a serious problem, especially when the loop passes round a number of small diameter of pulleys and turn back on themselves. Cable splicing, particularly in the case of wire ropes, involves specialist know-how and skills. It is believed that such an operation could not be achieved, so to speak, on the vehicle or transfer station.
The loading and unloading platform according to the invention is particularly, but not exclusively, adopted for use as a transfer station. The transfer station may be in the form of a concrete permanent structure with no access for the underneath of the platform. Thus, cable systems which employ cables passing under the platform are totally unsuitable for this application. Of course, in the case of a platform which does have access underneath the system as in the case of a vehicle floor according to the invention is still advantageous since this access may be difficult and hinder assembly of the cables and replacement.
Suitable splicing of wire ropes sufficient to convey heavy palletised loads without the cable unravelling in the region of the splice or failing through fretting or fatigue seems difficult, if not impossible, if carried out on or under the vehicle. If the closed loops are spliced under factory conditions as sub-assemblies, it is difficult to see how they could be fitted to the vehicle or transfer station in the case of the known conveyors previously referred to.